A computer program listing appendix containing the source code of a computer program that may be used with the present invention is incorporated herein by reference and appended hereto as one (1) original compact disk, and an identical copy thereof, containing a total of 473 files as follows:
1. Field of the Invention
The present invention is broadly concerned with apparatus for determining deformation in vehicle bodies and the like, using a laser scanning apparatus in conjunction with a plurality of coded targets suspended from (or in known relationship to) known reference points on the vehicle to calculate three dimensional spatial coordinates defining the actual positions of the targets, and to compare such calculated positions with manufacturer-provided specification values. More particularly, the invention is concerned with such apparatus and corresponding methods wherein use is made of a stationary central laser assembly including respective emitter lasers and corresponding parabolic collectors and associated detectors, a pair of upright, rotatable mirrors, and on-board scanner electronics all located within an enclosed housing.
Use of parabolic collectors has been found to enhance the detected signal strength, thus permitting more accurate vehicle repair.
2. Description of the Prior Art
In the past, vehicles such as automobiles have structural frames on which body panels and the like were built. Repair of accidental vehicle damage often involved straightening the frame and reshaping or replacing body panels. In order to meet government-imposed fuel consumption standards, unibody construction was adopted for many vehicles. In a unibody vehicle, no distinct frame exists apart from the body panels; instead, like an egg carton, the panels together form a xe2x80x9cunibodyxe2x80x9d, with consequence substantial weight savings.
With either form of vehicle, frame or unibody, repair is greatly speeded with improved quality, by use of a frame (and unibody) straightening machine such as described in U.S. Pat. No. RE 31,636. While such straightening machines are highly effective, such machines do not by themselves provide information as to the extent of straightening to be accomplished. Vehicles currently have manufacturer-provided reference points, such as reference openings or holes located at established points on the vehicles. Manufacturers also provide specifications for the correct three-dimensional spatial locations of these reference points relative to each other. Thus, if a vehicle is damaged, these reference points may be moved from their normal or xe2x80x9cspecificationxe2x80x9d positions with respect to each other. Most, if not all, vehicle frame and unibody straightening jobs require return of the vehicle reference points to within manufacturer specifications.
U.S. Pat. No. 5,801,834 describes a significant advance in the vehicle straightening art, and apparatus in accordance therewith has been commercialized by Chief Automotive Systems of Grand Island, Nebr. Specifically, this patent discloses a laser generating unit located beneath a vehicle and in an orientation for sweeping laser beams across the reflective surfaces of coded targets suspended from or in known relationship to the vehicle reference points. Preferably, a laser beam is split into two beams using a 50/50 beam splitter, with each beam then being directed to a rotating mirror. The rotating mirrors direct the laser beams in a 360xc2x0 circle, with both beams being directed in a single plane. Each laser beam is reflected back to its source when it strikes the reflective stripes of the coded targets. These reflected beams are registered as xe2x80x9conxe2x80x9d events (or counts) by the electronics onboard the laser measuring device. A counter counts the number of counts (as measured by an oscillator) from zero to the edge of each reflective/non-reflective border on the targets. An associated microprocessor receives the count information for each target and computes the angle from the center of each mirror to the center of each target. With the two angle measurements (one for each mirror and target) and the known baseline between the two mirrors, the planar (X, Y) coordinates of each reference hole are computed using trigonometry. The third coordinate (Z) is calculated using Z-coordinate representative sizing of the reflective and non-reflective strips on the coded targets. The actual three-dimensional spatial coordinates of each reference hole relative to a calculated point and plane are determined and displayed by the computer, along with the deviation from the normal or specification value provided by the vehicle manufacturer""s data. With this information, the operator may then straighten the frame or unibody, with successive measurements being taken to monitor the progress of the straightening operation and determination of when the frame or unibody is properly straightened.
It will be appreciated that the system described in the ""834 patent assumes that all of the vehicle targets will be essentially in plumb. However, in practice this is not always the case. For example, targets may not assume a plumb orientation owing to interference between the targets and vehicle components, particularly with damaged vehicles. Furthermore, many straightening shops are operated in open air so that the cantilever-suspended targets are subject to wind-induced oscillations. Whatever the cause, non-plumb targets detract from the desirable degree of accuracy which can be obtained using scanning laser devices of the type described in the ""834 patent.
In response to this problem, Chief Automotive introduced an improved Velocity(copyright) scanner employing vertically spaced apart scanning laser beams, thereby permitting determination of whether individual ones of the coded targets are in plumb relative to the vehicle, and the extent of any target inclination. This scanner is a decided improvement over single beam scanners.
Generally, laser vehicle alignment scanning systems generate high frequency laser beams which are detected in an analog fashion by strategically placed detectors. A potential problem in such systems is the presence of ambient light which may interfere with proper detection of the desired high frequency laser beam(s). One strategy to avoid ambient light interference involves cutting off a lower frequency portion of the detected signal in an effort to eliminate ambient light noise. However, this inevitably lowers the signal strength. As a consequence, a compromise must be made between signal strength and noise from ambient light interference.
There is accordingly a need in the art for vehicle repair laser scanning apparatus and methods having improved detection devices which have increased signal to noise ratios.
The present invention overcomes the problems outlined above, and provides an improved laser scanning system, and corresponding methods, for determining frame or unibody alignment of a vehicle. The system includes a scanning apparatus together with at least one reflective laser beam target adapted for placement in a known relationship relative to a selected reference point on a vehicle to be scanned. The scanning apparatus has a laser assembly operable to direct laser beams toward the vehicle target, and corresponding detector assemblies for receiving reflected laser beams from the target. Preferably, the laser assembly is operable to direct a pair of individual laser beams spaced vertically from each other by a known distance toward the target, and to detect the reflected beams from the target. In this way, using a microprocessor operably coupled with the scanning apparatus, it is possible to calculate individual, upper and lower, three-dimensional spatial coordinates of the target using the respective vertically spaced apart laser beams. This in turn permits determination of whether the target is truly in plumb (i.e., vertical), and the extent of deviation from plumb for the target. A particular feature of the scanning apparatus is the use of detector assemblies each comprising a substantially parabolic reflective surface together with a strategically located radiation detector position substantially at the focal point of the reflective surface.
In preferred forms, the laser assembly includes a pair of laser units, with each laser unit including a pair of vertically spaced apart lasers. The laser assembly is preferably stationary, with the overall apparatus including a pair of rotating mirror assemblies respectively located on opposite sides of the laser assembly. Each such mirror assembly comprises an upright mirror having a relatively wide reflective surface and a relatively narrow reflective edge; this permits discrimination between reflections from the wide mirror surfaces versus the narrow reflected edge surfaces. The detector assemblies advantageously include a block presenting an outboard parabolic reflective surface with a pair of vertically spaced apart openings therethrough; the associated upper and lower lasers are positioned so as to direct laser radiation through the block openings.
In practice, a plurality of reflected targets form a part of the system, and are suspended from individual reference points on the vehicle. Each of the targets is individually coded so that the scanning apparatus can discriminate between the targets. Preferably, each target has vertical endmost reflective stripes or xe2x80x9cstrikesxe2x80x9d, together with a pair of obliquely oriented reflective stripes between the endmost stripes.
Preferably, the components of the scanning apparatus, and particularly the laser assembly, mirror assemblies, detectors and on-board electronics are housed within an enclosed housing. This assures that the scanning apparatus can be used in a shop environment with a minimum of contamination from ambient dust or the like.
The parabolic detector assemblies give increased signal-to-noise ratios as compared wit conventional detectors, thereby giving improved alignment accuracy.